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More Colorado drivers in fatal crashes positive for pot, study says

A cannabis plant at a Denver grow house. (Seth McConnell, The Denver Post)

Two new University of Colorado studies paint an ominous picture of the direction of the state since marijuana commercialization, but neither provides conclusive evidence that legal pot is causing harm.

One study shows more drivers involved in fatal car accidents in Colorado are testing positive for marijuana — and that Colorado has a higher percentage of such drivers testing positive for pot than other states even when controlled for several variables. But the data the researchers use does not reveal whether those drivers were impaired at the time of the crash or whether they were at fault.

"The primary result of this study may simply reflect a general increase in marijuana use during this ... time period in Colorado," the study's authors write.

The other study shows that perceptions of marijuana's risk have decreased across all age groups with the boom in marijuana businesses in the state. The study also finds that near-daily marijuana use among adults increased significantly starting in 2009, relative to states without medical marijuana laws. But the study's authors acknowledge that they cannot show Colorado's marijuana laws are the reason for the shifts in attitudes and use.

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"Even though causality cannot be established, Colorado would be wise to implement prevention efforts regarding marijuana and make treatment for those with marijuana use disorders more broadly available," the study concludes.

Both studies received federal funding and were published online last month at the journal Drug and Alcohol Dependence. They mark the latest attempts to answer vexatious questions about how legal, commercially sold marijuana will impact the state.

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The studies begin their analyses several years prior to the 2009 boom in medical marijuana dispensaries. Both conclude their analyses in 2011 — the latest year for which data are available but prior to the 2012 legalization of recreational pot.

Quantifying problems with stoned driving has particularly stumped Colorado authorities, making the new study on fatal crashes — led by CU School of Medicine researcher Stacy Salomonsen-Sautel — especially notable.

The study found that, in 2011, the proportion of drivers in fatal crashes in Colorado testing positive for marijuana had risen to 10 percent — up from 5.9 percent in early 2009. In states without medical marijuana laws, 4.1 percent of fatal-crash drivers tested positive in 2011 — almost identical to the numbers from early 2009. Overall traffic fatalities in Colorado fell slightly during that period.

The Colorado State Patrol only just this year began keeping track of marijuana-impaired driving arrests. So far this year, 228 people have been cited in impaired-driving cases involving marijuana. Those cases make up about 13 percent of total impaired-driving citations issued by the State Patrol.

John Ingold: 303-954-1068, jingold@denverpost.com or twitter.com/john_ingold